The use of treadwear indicators is not new and the use of treadwear indicators is mandated by law in many countries. A variety of such indicators are known. Once such type employs colored means, such as colored rubber or colored fibers, below the tread for a visual indicator of wear. Other types use tie-bar type elements in the tread grooves. When required by law, the upper surface of the tread wear indicator must be located at a height of 1.6 mm from the base of the groove in which the wear indicator is located.
The practical problem with the colored indicators of the type mentioned is that there is way for the operator to determine the level of wear until the tire is worn. When the tire employs the tie-bar type wear indicator, since the wear indicator is the same color as the remaining part of the tread, it can be difficult to determine the level of wear.